In such a type of operation, an endoscope formed of a thin optical tube is inserted into the patient's abdomen through a small incision performed at the level of the patient's abdomen. The optical tube is generally connected to an external video camera. Other incisions may be performed to introduce surgical instruments handled by a surgeon. The endoscope is used to visualize the patient's internal organs and the surgical instruments. Since the surgeon generally has both hands occupied by the surgical instruments, an assistant is necessary to maintain the endoscope in a desired position.
Robotic systems have been developed to handle the endoscope instead of the assistant. Such systems are generally formed of massive, complex, and expensive robots comprising a base attached to the ground and an arm handling the endoscope. In the limited space of an operation table, the base of such a robot takes up a considerable place next to the patient. Further, the robot's arm maintaining the endoscope may hinder the access to the patient's abdomen.
It is thus desirable to provide a system for positioning on a patient an observation and/or intervention instrument taking up a small volume to limit the space required in the operation theatre and clear the access to the patient as much as possible.
International patent application WO0105319 assigned to the Universite Joseph Fourier describes, in an embodiment, a system for positioning an observation and/or intervention device, for example, an endoscope. The system comprises a mount placed on the patient's body, supporting a trocar in which the observation and/or intervention device slides, the trocar being likely to pivot with respect to the mount. An actuator assembly controls the trocar movement with respect to the mount. It may be formed of pneumatic or hydraulic actuators, each actuator being directly connected to the mount and to the trocar. It may also be formed of cables. Each cable then extends between the trocar and a guide attached on the mount, and is driven at its free end by an actuator placed at a distance from the patient.
A disadvantage of such a system is the difficulty to impose significant movements to the trocar. Indeed, in the case where the actuators are placed directly on the mount, the volume taken up by the actuators limits the trocar movements. In the case where the actuators are placed at a distance from the patient, the trocar movements are obtained by the application of tractions of different amplitudes on the cables connected to the trocar. A difficulty then results, in large movements, from the high flexion angles imposed to the cables at the level of the guides. This may result in a fast deterioration of the cables. Further, with such a system, the forces exerted by the cables or the actuators on the trocar are the origin of a pressure exerted by the trocar on the patient's abdomen that may be undesirable. Another disadvantage of such a system is that it is generally not possible to remove the positioning system while leaving in place the trocar and the observation and/or intervention devices.